Floated gyroscope



Feb. 13, 1962 R. A. FALK FLOATED GYROSCOPE Filed April 8, 1959 INVENTOR ROBERT A. FALK ATTORNEY United States Patent 3,020,768 FLOATED GYROSCOPE Robert A. Falk, Forest Hills, N.Y., assignor to Sperry Rand Corporation, Great Neck, N.Y., a corporation of Delaware Filed Apr. 8, 1959, Ser. No. 805,053 13 Claims. (Cl. 74-5) The present invention relates to instruments embodying a floated element and, more particularly, is concerned with such an instrument, for example, a floated gyroscope, which is adapted for miniaturization and low temperature operation.

Floated gyroscopes are noted for accuracy, reliability and durability. They are characterized by a fluid-tight sealed assembly which encases a spinning gyrowheel.

,The assembly, in turn, is rotatably supported Within a fluid-filled container. The function of the fluid is to float the assembly in substantially neutral equilibrium so as to reduce to an arbitrary minimum the frictional forces acting :at the bearing supports for the assembly. The reduction and substantial elimination of such frictional forces imparts a high degree of rotational freedom to the assembly about its supporting axes whereby displacements about the supporting axes resulting from minute forces can be monitored accurately.

Especially in certain recent applications such as, for example, in inertial guidance systems for airborne vehicles, the reduction in size and Weight of floated gyroscope instruments is of singular importance. Such reduction in size and weight, however, should not be achieved at the expense of a corresponding reduction in gyrowheel angular momentum. As is well understood, it is desirable that the gyrowheel angular momentum be made as large as practical in order to enhance the accuracy of the instrument. It is also desirable that the assembly including the hermetically encased spinning gyrowheel be designed with a high degre of structural rigidity.

It should be noted that the average density of the assembly including the hermetically encased spinning gyro- Wheel increases for a given weight as its volume is decreased, v Inasmuch as the specific gravity of the flotation fluid must be commensurate with the average density or the assembly to be floated, as the assembly density increases so must also the specific gravity of the flotation fluid increase.

Flotation fluids having usefully high density are generally available. One common shortcoming generally associated with such prior art high density flotation fluids, however, is that these fluids solidify at relatively high temperatures, usually even at temperatures substantially higher than room temperature. The elevated solidification point imposes a severe handicap in the production, shipment and storage of the prior art flotation fluids. Once the gyroscope is filled with these fluids, it remains necessary that the filled gyroscope be kept at temperatures higher than the fluid solidification point to avoid risking permanent internal gyroscope damage which would be caused by the rapid change in fluid volume that normally occurs upon fluid solidification. It should also be noted that even where the delicate gyroscope structure is not damaged in the process of fluid solidification,

there remains therattendant disadvantage that relatively I 3,020,768 Patented Feb. 13, 1962 long warm up times are required to change the state of the solidified fluid to its normal liquid operating condition whereupon the associated and considerable latent heat must be supplied.

Another undesirable characteristic of prior art flotation fluids is the pronounced tendency to fissure at temperatures relatively slightly below the solidification temperature. Fissuring of the flotation fluid greatly endangers the delicate power leads located within the gyroscope which pass through the fluid. 7 Some of the desirable characteristics of a preferred flotation fluid are implicit in the foregoing discussion of the shortcomings of prior art fluids. For example, it is important that the preferred flotation fluid be characterized by the concurrently realizable physical properties of high density, low solidification point and resistance to fissure. Other characteristics such as low vapor pressure are also important but of primary concern is the requirement that all of the desirable physical properties of the flotation fluid be concurrently present. It is not enough that the different fractions, for example, of the same flotation fluid have different and respective ones of the desirable physical characteristics; the same fractions should have all.

The general object of the present invention is to provide a fluid-filled gyroscope adapted for miniaturization and suitable for use at low temperatures.

Another object of the present invention is to provide a fluid-filled gyroscope wherein the flotation fluid is characterized by the desired concurrent physical properties of high density, low solidification point, low vapor pressure and substantial resistance to fissure.

A further object is to provide a fluid-filled gyroscope wherein the fluid is characterized by low solidification point and controllable high density.

These and other objects of the present invention are achieved in apreferred embodiment by the provision of a gyroscope of the floated type wherein the flotation fluid comprises a suitably selected fraction of the bromotrifluoroethylene polymer hereinafter referred to as polybromo fluid. The selection of the polybromo fluid fraction primarily is determined by the density of the assembly to be floated in a given design. By conventional fractionation techniques, suitable individual fractions of the polybromo fluid can be isolated, each having a different respective specific gravity but similarly useful low solidification point, low vapor pressure and substantial resistance to fissure.

In the casev of certain present gyroscope designs requiring the use of flotation fluids of lower specific gravity than can be obtained by simple fractionation of the polybromo fluid, the present invention provides for the blending of the polybromo fluid with a second polymer fluid, such as, for example, polychlorotrifluoroethylene having the required vapor pressure and a specific gravity less than that of the polybromo fluid.

For a more complete understanding of the present invention, reference should be had to the following specification and to the drawing which is a simplified representation of a fluid-filled gyroscope embodiment of the presentinvention.

The floated gyroscope of the sole figure is of the miniature, direct reading, gyrocompass type. It is especially adapted for use on small mobile vehicles. Inasmuch as the specific details of construction of the floated gyroscope is of no particular moment in the case of the present invention, only a brief description will be given respecting basic structural features. A gyroscope of this type is disclosed in more detail in US. Patent 2,797,581, issued on July 2, 1957, in the name of Leslie F. Carter and assigned to the present assignee.

Binnacle 1 is a liquid-tight housing member for the gyrocompass having a main compartment 2 and an auxiliary compartment 3 containing an expansible diaphragm 4. Binnacle 1 is suitably mounted on the vehicle employing the gyrocompass. A liquid-tight spherical case 5, housing the spinning gyrowheel (not shown), is rotatably supported about axis 6 by trunnions 7 and 8 and gimbal ring 9.

Gimbal ring 9, in turn, is rotatably supported about axis 10 by upper and lower trunnions 11 and 12, respectively. Hollow float members 13 and 14 are affixed to gimbal ring 9. A fluid duct 15 interconnects main compartment 2 and diaphragm 4, both of which are com pletely filled with polybromo fluid. Diaphragm 4 acts as an expansion chamber for the fluid. The specific gravity of the fluid is that which is required to float totally immersed spherical case 5 in substantially neutral equilibrium so as to eliminate any loading on trunnions 7 and 8 and also to float gimbal ring 9 and its associated hollowed float members 13 and 14 in substantially neutral equilibrium so as to eliminate loading on the upper and lower trunnions 11 and 12.

The polybromo fluid which fills main compartment 2 and diaphragm 4 is produced by the polymerization of bromotrifluoroethylene utilizing a polymerization process similar to that disclosed in chapters 32 and 33 of Schlesser and Schram, Preparation, Properties and Technology of Fluorine and Organic Fluoro Compounds, National Nuclear Energy Series, volume VII-I, McGraw- Hill, 1951, dealing with the preparation of the polychlorotrifluoroethylene. The synthesis of the polybromo fluid follows the general method described in the aforementioned book, differing therefrom only in certain details. The polybromo fluid is similar chemically to polychlorotrifluoroethylene with bromine substituted for chlorme.

The synthesis may be divided into the four phases of polymerization, distillation, stabilization, and fractionation. The polymerization, distillation, and fractionation phases of the synthesis of the polybromo fluid are directly analogous to those of the prior art method for the prep aration of polychlorotrifluoroethylene. The stabilization phase, however, must be conducted under considerably different and milder conditions.

The crude polybromo fluid obtained as a result of the polymerization and distillation phases of the prior art method is stabilized with cobaltic fluoride in a special mixing apparatus. The mixing apparatus comprises a stainless steel container equipped with a close-fitting scraping stirrer, driven by a high torque, low speed motor which is capable of stirring a very pasty mass at approximately 150 C. The mixing apparatus is also equipped with means for automatically maintaining the preferred temperature of approximately 150 C. during the mixing operation.

The crude polybromo fluid is stirred slowly and treated stepwise with several portions of the cobaltic fluoride. A sample amount of the polybromo fluid is then extracted with acetone, filtered and tested with a solution of 2% potassium permanganate. Should decolorization occur, additional portions of cobaltic fluoride are added to the mixture until the polybromo fluid no longer decolorizes upon the addition of the permanganate after standing at C. for ten minutes. The polybromo fluid is then separated from the cobalt salts by means of a suitable filter such as a Buchner filter. The polybromo residue adhering to the filter is then washed repeatedly with a. solvent such as carbon tetrachloride. The polybromo fluid is recovered from solution with the carbon tetrachloride solvent by evaporating the solvent.

It is important that the above-described stabilization reaction proceed exothermically and that the addition of cobaltic fluoride be slow, especially initially. Care must be taken that the reaction temperature does not exceed approximately 165 C. to inhibit the excessive evolution of bromine.

Although polybromo fluid is somewhat similar chemically to polychlorotrifluoroethylene and is prepared by an analogous process, the polybromo fluid has several important physical properties, not shared by polychlorotrifiuoroethylene, which are uniquely advantageous for use in floated gyroscopes. Such characteristics include specific gravities which vary from about 2.1 to about 2.5, depending on the fraction selected. Each of the fractions share the important and beneficial characteristics of low solidification point (about 65 F. or below), usefully low vapor pressure, and substantial resistance to fissure.

Another physical characteristic of substantial importance and not common to polychlorotrifluoroethylene is that as temperatures are reduced to the solidification point and beyond, the polybromo fluid exhibits no pronounced tendency to quickly crystallize to a rigid solid but rather solidifies to a glass. The glassing of the polybromo fluid, as opposed to crystallization, obviates any great change in volume as the solidification point temperature is traversed. Consequently, the volume of the polybromo fluid changes substantially linearly with respect to temperature minimizing to a considerable extent any tendency toward fissuring of the solidified fluid.

To exemplify the desirable physical properties of the polybromo fluid, one fraction thereof prepared in accordance with the above-described procedure was found to have a solidification point of approximately 65 F., a fissure point below -70 F., a density of approximately 2.25 grams/cm. at 165 F. and a vapor pressure of about microns at F. The advantages attributable to the low solidification point, high density and low fissure point have previously been pointed out. The significance of the low vapor pressure (no higher than 100 microns at about 165 F.) is that handling of the polybromo fluid prior to and including the operation for filling the floated gyroscope is greatly facilitated. It can be seen that the resulting density of the fluid in the gyroscope after completion of the filling operation would be exceedingly diflicult to control in the event that the fluid, prior to filling, contained highly volatile low molecular Weight fractions. The evolution of such volatile fractions would considerably impede the close control of specific gravity of the fluid.

Inasmuch as the lowest specific gravity of the low vapor pressure fractions of the polybromo fluid is about 2.1, provision must be made in the case of certain present day floated gyroscope designs for reducing somewhat the specific gravity of the flotation fluid to be compatible with the predesigned density of the gyroscope assembly to be floated. The present invention provides for a relatively simple blending method for tailoring the specific gravity of the polybromo fluid to match the density of a given gyroscope assembly design by the addition of a suitable low vapor pressure and low specific gravity polymer solvent such as polychlorotrifluoroethylene. Additionally, some control over the viscosity of the blended fluid may be had by the addition of a commercially available resin. Such blending yields fluid mixtures having specific gravities in the range from about 1.85 to about 2.5 at 165 F., a solidification point in the range from about 65 F. to about 5 F., and a vapor pressure in the range from about 20 to about 180 microns at 165 F.

The following blending procedure is typical and has been used to produce a polybromo fluid blend having a specific gravity of about 1.9370 grams/cm. at 165 F., a solidification point about 65 F., a vapor pressure about 20 microns at 165 F. and a viscosity of about 1400 centipoise at 165 F. The blend constituents comprise 750 grams of a polybromo fluid fraction having a density of 2.2515 grams/cm? at 165 F., 2041 grams of commercially available polychlorotrifluoroethylene such as KF Alkane 10157 having a density of about 1.8445 grams/cm. at 165 F., and 272 grams of a suitable polymeric thickener such as KF #800 resin. KF Alkane 10157 and KF #800 resin are manufactured by the Minnesota Mining and Manufacturing Company.

The KF #800 resin should be dried for several hours at about l20160 F. to completely dehydrate it before use in the blending operation. The polybromo fluid and polychlorotrifluoroethylene are mixed together and gradually heated to about 140 C., with stirring, while the resin is added in small portions. After mixing, the temperature of the blend is maintained at about 140 C. for four hours. The fluid is then maintained at such temperature for an additional two hours.

The fluid blend is then gravity filtered through a 100 mesh stainless steel screen. It is then vacuum filtered, at 5 to 20 microns of mercury, preferably through a 30 micron sintered glass filter. Final filtration is accomplished by filtering the fluid blend through a 5 micron stainless steel filter at the same vacuum pressure as used previously. Resultant fluid blends having a lower or higher specific gravity than that obtained by the abovedescribed blending procedure may be produced by the addition of more or less polychlorotrifluoroethylene, respectively.

From the preceding it can be seen that the objects of the present invention have been achieved by the provision of the combination of polybromo fluid in a gyroscope of the floated type. The specific gravity of the polybromo fluid may be selected to be compatible with the density of specific gyroscope float assembly designs by conventional fractionation techniques. Provision is made in the present invention for greater latitude in the lowering of the specific gravity and adjustment of the viscosity of the polybromo fluid by a technique for blending the polybromo fluid with a suitable low vapor pressure solvent such as polychlorotrifluoroethylene and athickener.

While the invention has been described in its preferred embodiments, it is understood that the words which have been used are words of description rather than of limitation and that changes within the purview of the appended claims may be made Without departing from the true scope and spirit of the invention in its broader aspects.

What is claimed is:

1. An instrument of the floated type comprising in combination a first liquid-tight housing member, a second liquid-tight housing member, means for rotatably supporting said second housing member within said first housing member, and a fluid having a density in the range from about 2.1 to about 2.5 for immersing said second housing member and for floating said immersed second housing member in substantially neutral equilibrium, said fluid remaining in a fluid state at a temperature of about 65 F. and being a polymeric composition of matter comprising polybromotrifluoroethylene.

2. An instrument of the floated type comprising in combination a first liquid-tight housing member, a second liquid-tight housing member, means for rotatably supporting said second housing member within said first housing member and a fluid having a density in the range from about 2.1 to about 2.5 for immersing said second housing member and for floating said immersed second housing member in substantially neutral equilibrium, said fluid remaining in a fluid state at a temperature of about 65 F. and being a polymeric composition of matter consisting essentially of polybromotrifluoroethylene.

3. A gyroscope of the floated type comprising in combination a first liquid-tight housing member, a second liquid-tight member for housing a gyrowheel, said second housing member and the contents thereof having a total density in the range from about 2.1 to about 2.5, means for rotatably supporting said second housing member within said first housing member, and a fluid for totally immersing said second housing member and for floating said immersed second housing member in substantially neutral equilibrium, said fluid remaining in a fluid state at a temperature of about 65 F. and being a polymeric composition of matter comprising polybromotrifluoroethylene.

4. A low temperature subminiaturized gyroscope of the floated type comprising in combination a first liquidtight housing member, a second liquid-tight member for housing a gyrowheel, means for rotatably supporting said second housing member within said first housing member, anda fluid for totally immersing said second housing member and for floating said immersed second housing member in substantially neutral equilibrium, said fluid consisting essentially of polybromotrifluoroethylene.

5. An instrument of the floated type adapted to withstand frigid environmental temperatures comprising in combination a first liquid-tight housing member, a second liquid-tight housing member, means for rotatably supporting said second housing member within said first housing member, and a fluid having a density in the range from about 1.85 to about 2.5 for immersing said second housing member and for floating said immersed second housing member in substantially neutral equilibrium, said fluid comprising a mixture of polybromotrifluoroethylene and polychlorotrifluoroethylene.

6. An instrument of the floated type adapted to withstand frigid environmental temperatures comprising in combination a first liquid-tight housing member, a second liquid-tight housing member, means for rotatably supporting said second housing member within said first housing member and a fluid having a density in the range from about 1.85 to about 2.5 for immersing said second housing member and for floating said immersed second housing member in substantially neutral equilibrium, said fluid consisting essentially of a mixture of polybromotrifluoroethylene and polychlorotrifluoroethylene.

7. A gyroscope of the floated type adapted to withstand frigid environmental temperature comprising in combination a first liquid-tight housing member, a second liquid-tight member for housing a gyrowheel, said second housing member and the contents thereof having a total density in the range from about 1.85 to about 2.5, means for rotatably supporting said second housing member Within said first housing member, and a fluid for totally immersing said second housing member and for floating said second housing member in substantially neutral equilibrium, said fluidcomprising a mixture of polybromotrifluoroethylene and polychlorotrifluoroethylene.

8. A low temperature subminiaturized gyroscope of the floated type comprising in combination a first liquid-tight housing member, a second liquid-tight member for housing a gyrowheel, means for rotatably supporting said second housing member within said first housing member, and a fluid for totally immersing said second housing member and for floating said immersed second housing member in substantially neutral equilibrium, said fluid consisting essentially of a mixture of polybromotrifluoroethylene and polychlorotrifluoroethylene.

9. The composition of matter which is the fluid blend comprising polybromotrifluoroethylene and polychlorotrifluoroethylene.

10. The composition of matter which is the fluid blend consisting essentially of polybromotrifluoroethylene and polychlorotrifluoroethylene.

11. As a flotation fluid for use in an instrument of the floated type, the composition of matter which is the fluid blend comprising polybromotrifluoroethylene and polychlorotrifluoroethylene.

12. As a flotation fluid for use in a gyroscope of the floated type, the composition of matter which is the fluid blend consisting essentially of polybromotrifiuoroethylene and polychlorotrifluoroethylene.

13. A flotation fluid for use in a gyroscope of the floated type, said fluid having the concurrent physical properties of a specific gravity in the range from about 1.85 to about 2.5 at 165 F. a solidification point in the range from about 65 F. to about 5 F. and a vapor pressure in the range from about 20 to about 180 microns at 165 F., said fluid being the composition of matter which is the fluid blend consisting of polybromotrifiuoroethylene, polychlorotrifiuoroethylene and any additive not subversive of the above physical properties.

References Cited in the tile of this patent UNITED STATES PATENTS 

1. AN INSTRUMENT OF THE FLOATED TYPE COMPRISING IN COMBINATION A FIRST LIQUID-TIGHT HOUSING MEMBER, A SEOND LIQUID-TIGHT HOUSING MEMBER, MEANS FOR ROTATABLY SUPPORTING SAID SECOND HOUSING MEMBER WITHIN SAID FIRST HOUSING MEMBER, AND A FLUID HAVING A DENSITY IN THE RANGE FROM ABOUT 2.1 TO ABOUT 2.5 FOR IMMERSING SAID SECOND HOUSING MEMBER AND FOR FLOATING SAID IMMERSED SECOND HOUSING MEMBER IN SUBSTANTIALLY NEUTRAL EQUILLIBRIUM, SAID FLUID REMAINING IN A FLUID STATE AT A TEMPERATURE OF ABOUT -65*F, AND BEING A POLYMERIC COMPOSITION OF MATTER COMPRISING POLYBROMOTRIFLUOROETYLENE. 